As for the conventional method for producing cellular molded article of synthetic resin with surface skin of this kind, for example, (a) so-called simultaneous molding in once is known, in which thermoplastic resin skin material is set in any one of two mold parts, and after clamping the mold parts, expanded beads are charged in the molding chamber, and then expanded additionally for melt bonded together by steam heating, along with making melted bonding with the said thermoplastic resin skin material. In this method when the said two mold parts can be opened and clamped toward vertical direction, the said one mold part has to be the lower part to make setting of the said thermoplastic resin skin material easy.
(b) Moreover, in this simultaneous united molding, as shown in FIG. 28, it is common that the surface 5a of the said one mold part 5 is smoothed, and that the surface 3a of the said thermoplastic resin skin material 3 is made a mat processing with a prescribed roughness and performed to form fine and uniform unevenness 19. In this case, when after charging expanded beads 8 in the said molding chamber 7 and cellular molding these beads 8 by steam heating, the prescribed range D of the surface 3a of the said thermoplastic resin skin material 3 is pressed by the surface 5a of the said one mold 5 harder than the other range E by expanding force F of the said expanded beads 8 from the backside 3b.
Here, since the said thermoplastic resin skin material 3 is softened by steam heating, as shown in FIG. 29, the fine unevenness 19d which is even finer than the fine unevenness 19 formed in advance by mat processing is formed in the said range D which is pressed harder as above-mentioned. Also, the said the other range E is pressed against the surface 5a of the said one mold part 5 by the expanding force which is smaller than that pressing the range D. Therefore, the fine unevenness 19e which is about as fine as or a little finer than the fine unevenness 19 formed in advance by the said mat processing is formed in the other range E. However, the fine unevenness 19d in the said range D is finer as a result of being pressed harder against the surface 5a of the said one mold part 5, the range D appears as circular so-called beads pattern when looked over. This is disadvantageous as it deteriorates the appearance of the obtained cellular molded article of synthetic resin having surface skin 51.
(c) As the example of conventional method to solve such problem, the method in which, as shown in FIG. 30, laminated sheet 23 which comprises of thermoplastic resin sheet 53 whose surface 53a is formed to the fine unevenness 19 by mat processing and the thermoplastic resin extruded foam sheet 54 which is attached to the backside 53b of the thermoplastic resin sheet 53 is used as the said thermoplastic resin skin material 3, and the sheet 23 is set as the said thermoplastic resin sheet 53 surface will come in contact with the said one mold part 5 and the said thermoplastic resin extruded foam sheet 54 surface will come in contact with the said expanded beads 8, and other processes are the same as the above-mentioned is known.
In this method, when the said thermoplastic resin extruded foam sheet 54 is pressed from its backside 54b by expanding force F of the said expanded beads 8 at the cellular molding process of the said expanded beads 8, this thermoplastic resin extruded foam sheet 54 functions as so-called cushioning material. Therefore, it is hard for the pressing force F to work on the surface 53a of the said thermoplastic resin 53, consequently, the above-mentioned beads pattern does not appear.
(d) In addition to the above-mentioned simultaneous united molding, for example, the so-called afterward attached molding, in which cellular molded article of synthetic resin 2 and thermoplastic resin skin material 3 are set between two mold parts, and when clamping the mold parts and pressurizing them, these cellular molded article of synthetic resin 2 and thermoplastic resin skin material 3 are united by heat and/or adhesives is known.
In FIG. 31, the case when the said cellular molded article of synthetic resin 2 and thermoplastic resin skin material 3 are melt bonded and united by heat is shown. In this case, as the above-mentioned, it is common that the surface 15a of the one mold part 15 which will come in contact with the said thermoplastic resin skin material 3 is smoothed and that mat processing of a prescribed unevenness is more or less uniformly performed to form the fine unevenness 19 on the surface 3a of the said thermoplastic resin skin material 3. On the other hand, it is not common that the surface 2a of the said cellular molded article of synthetic resin 2 is smoothed. Also the case of uniting cellular molded article of synthetic resin 2 with thermoplastic resin skin material 3 by adhesive existing between them without heat, or the case of uniting by both heat and adhesive is in similar conditions as above-mentioned.
However, in the conventional example of above-mentioned (a), since the expanded beads are expanded by the said steam heating, drain (moisture) may remain in the said molding chamber during this steam heating process and before expanding process of the said expanded beads. Therefore, the disadvantage is that this remaining drain causes poor melt bonding of the expanded beads in the cellular molded article of synthetic resin obtained by cellular molding process of the said expanded beads.
In the conventional example of above-mentioned (c), the disadvantage is that, since the said thermoplastic resin extruded foam sheet 54 has to be separately produced by foamed extrusion process, and stuck to the said thermoplastic resin sheet 53 beforehand, the production process is complicated and the production efficiency is poor.
Also, in the conventional example of above-mentioned (d), since the surface 2a of the said cellular molding articles of synthetic resin 2 is not smooth, as shown in FIG. 31, the prescribed range D of the surface 3a of the said thermoplastic skin material 3 is pressed from the backside 3b against the surface 15a of the said one mold part 15 harder than the other range E by pressurizing force G when melt bonding and uniting this cellular molded article of synthetic resin 2 with thermoplastic resin skin material 3 are operated.
Therefore, as is the case of simultaneous united molding of above-mentioned (b), the said range D appears as circular so-called beads pattern when looked over, and it is disadvantageous as it deteriorates the appearance of the obtained cellular molded article of synthetic resin having surface skin 51. Also, when cellular molded article of synthetic resin 2 and thermoplastic resin skin material 3 are united by both heat and adhesive, similar beads pattern is observed. Moreover, when they are united by adhesive without heat, the similar beads pattern is observed, and it is disadvantageous as above-mentioned.
This invention has been accomplished in consideration of above-mentioned disadvantages, and aims to provide a method for producing cellular molded article of synthetic resin having surface skin which comprises of cellular molded article of synthetic resin obtained by cellular molding of expanded beads in which poor melt bonding does not occur and thermoplastic resin skin material united with this cellular molded article which has excellent appearance without beads pattern on its surface, and which has good production efficiency, and a mold used for producing thereof.